Process for reducing unstable end-groups in fluorinated polymers

ABSTRACT

A process for reducing the number of unstable end-groups in a fluorinated polymer is disclosed, said process comprising reacting a fluorinated polymer comprising unstable end-groups with fluorine in the presence of at least one (per)haloolefin comprising at least one carbon-carbon double bond and having at least one fluorine or chlorine atom on either one of the carbon atoms of said double bond. The fluorinated polymer may be selected from those polymers comprising recurring units derived from at least one ethylenically unsaturated fluorinated monomer or from fluorinated polyethers.

This application is a U.S. national stage entry under 35 U.S.C. §371 ofInternational Application No. PCT/EP2012/073037 filed Nov. 20, 2012,which claims priority to European application EP11191272.1 filed Nov.30, 2011. The entire contents of these applications are explicitlyincorporated herein by this reference.

TECHNICAL FIELD

The invention relates to a process for reducing unstable end-groups influorinated polymers.

BACKGROUND ART

Fluorinated polymers are known in the art. Fluorinated polymers aregenerally known for their chemical and thermal stability. Said thermaland chemical stability is however negatively affected by the presence ofionic end-groups in the polymeric chain, for instance —CH₂OH, —COF,—COOH type end-groups. For instance, —COF and —COOH type end-groups areknown to initiate the so-called “unzipping reaction”, wherein startingfrom these end-groups, the main chain of the fluorinated polymerprogressively disaggregates following the reaction scheme sketched herebelow:R_(f)—CF₂COOH+.OH→R_(f)—CF₂.+CO₂+H₂OR_(f)—CF₂.+.OH→R_(f)—CF₂OH→R_(f)—COF+HFR_(f)—COF+H₂O→R_(f)—COOH+HFwherein R_(f) represents the fluorinated polymer chain.

Several methods have been proposed in the past aiming at improving thestability of fluorinated polymers by reduction of the number of unstableend-groups.

GB 1210794 (E.I. DUPONT DE NEMOURS AND COMPANY) Oct. 28, 1970 disclosesa process for the stabilization of high molecular weight fluorocarbonpolymers in the solid state (as particulate or pre-molding form or asmolded articles) by contacting said polymers with a fluorine radicalgenerating compound (e.g. gaseous fluorine) in the absence of oxygen.

U.S. Pat. No. 4,743,658 (E.I. DUPONT DE NEMOURS AND COMPANY) May 10,1988 discloses a process for the stabilization oftetrafluoroethylene/perfluoroalkylvinylether copolymers by fluorinationof the same under the form of pellets by solid/gas reaction withfluorine gas.

These processes however generally require the use of high temperature toobtain the full conversion of the unstable-end groups.

Also it is known in the art a process for the stabilization of amorphouspolymers. EP 1256591 A (AUSIMONT S.P.A.) Nov. 13, 2002 and EP 1256592 A(AUSIMONT S.P.A.) Nov. 13, 2002 disclose a process for the stabilizationof amorphous perfluorinated polymers, wherein the polymer is firstdissolved in a suitable solvent so as to obtain a solution having aconcentration of from 0.5 to 15% by weight, and then said solution issubmitted to fluorination with elemental fluorine in the presence of UVradiation. Fluoropolymers stabilized according to such method areendowed with a substantial absence of unstable polar end groups, i.e.undetectable by FT-IR spectroscopy.

GB 1226566 (MONTECATINI EDISON SPA) Apr. 4, 1967 discloses a process forthe removal of ionic end-groups in perfluorinated polyethers whichcomprises fluorination of the perfluorinated polyether in a liquid phasewith fluorine at a temperature of 100 to 350° C.

It has now been found that the reduction of unstable end-groups can beefficiently performed on a fluorinated polymer under mild reactionconditions and with high conversion of the unstable end-groups bytreating said fluorinated polymer with fluorine in the presence of a(per)haloolefin.

DISCLOSURE OF INVENTION

It is thus an object of the present invention to provide a process forreducing the number of unstable end-groups in a fluorinated polymer.

The process of the invention comprises reacting a fluorinated polymercomprising unstable end-groups with fluorine in the presence of at leastone (per)haloolefin comprising at least one carbon-carbon double bondand having at least one fluorine or chlorine atom on either one of thecarbon atoms of said double bond.

The expression “unstable end-groups” is used to indicate chainend-groups of the following types —CH₂OH, —COF, —COOH, —CONH₂, —CONR₂,—COOR, wherein R indicates a C₁-C₂₀ alkyl or fluoroalkyl group.Preferably the expression “unstable end-groups” is used to indicatechain end-groups comprising a —C(O)— functional group, thus end-groupsselected from the group consisting of —COF, —COOH, —CONH₂, —CONR₂,—COOR, wherein R is as defined above.

The term “fluorinated” is used herein to refer to compounds (e.g.monomers, polymers, polyethers etc.) wherein at least 95%, 98% and even99% of hydrogen atoms have been replaced by fluorine atoms and/orhalogen atoms. The term includes compounds wherein a small amount ofhydrogen atoms of less than 5%, 2% and even 1%, may still be present.

The term “perfluorinated” is used herein to refer to compounds (e.g.monomers, polymers, polyethers etc.) that are free of hydrogen atoms,i.e. wherein at least 99.5% of hydrogen atoms, preferably at least 99.8%of hydrogen atoms have been replaced by fluorine atoms and/or halogenatoms.

The expression “fluorinated polymers” as used in the presentspecification includes both polymers comprising recurring units derivingfrom the addition polymerization of at least one ethylenicallyunsaturated fluorinated monomer as well as fluorinated polyethers.

In one embodiment fluorinated polymers are those comprising recurringunits derived from at least one ethylenically unsaturated fluorinatedmonomer. Typically these fluorinated polymers have a number averagemolecular weight (M_(n)) of at least 10000, preferably at least 20000.The molecular weight (M_(n)) is generally not higher than 1000000,preferably not higher than 500000 and even more preferably not higherthan 250000.

Non limiting examples of suitable ethylenically unsaturated fluorinatedmonomers are:

-   -   C₂-C₈ perfluoroolefins, such as tetrafluoroethylene,        hexafluoropropylene;    -   chloro- and/or bromo- and/or iodo-C₂-C₆ fluoroolefins, like        chlorotrifluoroethylene;    -   fluoroalkylvinylethers of formula CF₂═CFOR_(f1) in which R_(f1)        is a C₁-C₆ fluoro- or perfluoroalkyl, e.g. —CF₃, —C₂F₅, —C₃F₇;    -   fluoro-oxyalkylvinylethers of formula CF₂═CFOX₁, in which X₁ is        a C₁-C₁₂ fluoroxyalkyl, or a C₁-C₁₂ perfluorooxyalkyl having one        or more ether groups, like perfluoro-2-propoxy-propyl;    -   fluoroalkyl-methoxy-vinylethers of formula CF₂═CFOCF₂OR_(f2) in        which R_(f2) is a C₁-C₆ fluoro- or perfluoroalkyl, e.g. —CF₃,        —C₂F₅, —C₃F₇ or a C₁-C₆ perfluorooxyalkyl having one or more        ether groups, like —C₂F₅—O—CF₃;    -   functional fluoro-alkylvinylethers of formula CF₂═CFOY₀, in        which Y₀ is a C₁-C₁₂ fluoroalkyl or perfluoroalkyl, or a C₁-C₁₂        fluorooxyalkyl, or a C₁-C₁₂ perfluorooxyalkyl, said Y₀ group        having one or more ether groups and Y₀ comprising a carboxylic        or sulfonic acid group, in its acid, acid halide or salt form;    -   fluorodioxoles, of formula (I):

-   -   wherein each of R_(f3), R_(f4), R_(f5), R_(f6), equal or        different each other, is independently a fluorine atom, a C₁-C₆        fluoro- or per(halo)fluoroalkyl, optionally comprising one or        more oxygen atom, e.g. —CF₃, —C₂F₅, —C₃F₇, —OCF₃, —OCF₂CF₂OCF₃.

Notable examples of fluorinated polymers that may advantageously bestabilized with the inventive process include tetrafluoroethylenecopolymers which comprise, in addition to recurring units deriving fromtetrafluoroethylene, recurring units deriving from of at least one othermonomer selected from the group consisting of hexafluoropropylene and/orperfluoro(alkyl vinyl ether) in which the linear or branchedperfluoroalkyl group contains 1 to 5 carbon atoms. Preferredperfluoro(alkyl vinyl ether)monomers are those in which theperfluoroalkyl group contains 1, 2, 3 or 4 carbon atoms. Mention may bemade in particular of tetrafluorethylene/hexafluoropropylene copolymers,tetrafluorethylene/perfluoro(alkyl vinyl ether) copolymers,tetrafluorethylene/hexafluoropropylene/perfluoro(alkyl vinyl ether)copolymers wherein the perfluoro(alkyl vinyl ether) is selected fromperfluoro(methyl vinyl ether) and/or perfluoro(propyl vinyl ether);tetrafluorethylene/perfluoro(methyl vinyl ether)/perfluoro(alkyl vinylether) copolymers wherein the perfluoroalkyl group of theperfluoro(alkyl vinyl ether) has at least 2 carbon atoms.

Another class of fluorinated polymers that may advantageously be treatedaccording to the inventive process includes copolymers comprisingrecurring units deriving from tetrafluoroethylene orchlorotrifluoroethylene and recurring units deriving from fluorodioxolesof formula (I) above. Preferred fluorodioxoles are selected from2,2-bis(trifluoromethyl)-4,5-difluoro-1,3-dioxole and2,2,4-trifluoro-5-trifluoromethoxy-1,3-dioxole.

Still another class of fluorinated polymers comprises polymerscomprising recurring units deriving from tetrafluoroethylene and/orchlorotrifluoroethylene and recurring units deriving from at least onefunctional monomer of formula CF₂═CF—O—(CF₂CF(CF₃)O)_(m)—(CF₂)_(n)SO₂Fand its acid or salt form wherein m is an integer equal to 0 or 1, n isan integer from 0 to 10, preferably from 1 to 4.

In another embodiment of the process the fluorinated polymer is afluorinated polyether. Fluorinated polyethers generally have a numberaverage molecular weight (M_(n)) of at least 400, preferably of at least450. The molecular weight (M_(n)) typically is not higher than 15000,preferably not higher than 10000.

Non-limiting examples of suitable fluorinated polyethers include thosecomprising one or more recurring units chosen among the group consistingof:

—CFXO—, wherein X is —F or —CF₃;

—CF₂CFXO—, wherein X is —F or —CF₃;

—CFXCF₂O—, wherein X is —F or —CF₃;

—CF₂CF₂CF₂O—;

—CF₂CF₂CF₂CF₂O—;

—(CF₂)_(k)—CFZ—O—, wherein k is an integer from 0 to 3 and Z is a groupof general formula —OR_(F)T₃, wherein R_(F) is a fluoropolyoxyalkylenechain comprising a number of recurring units from 0 to 10, saidrecurring units being chosen among the following: —CFXO—, —CF₂CFXO—,—CF₂CF₂CF₂O—, —CF₂CF₂CF₂CF₂O—, wherein each of X is independently —F or—CF₃, and T₃ is a C₁-C₅ perfluoroalkyl group, and mixtures thereof.

Notable examples of fluorinated polyethers that may conveniently besubjected to the inventive process are those comprising units selectedfrom the group consisting of:

-   -   —(CF₂O)_(a)—(CF₂CF₂O)_(b)—(CF₂—(CF₂)_(d)—CF₂O)_(c), wherein a, b        and c are integers up to 100, preferably up to 50, and d is        independently at each occurrence an integer equal to 1 or 2,        a≧0, b≧0, c≧0 and a+b>0; preferably, each of a and b are >0 and        b/a is comprised between 0.1 and 10;    -   —(C₃F₆O)_(e)—(CF₂CF₂O)_(b)—(CFXO)_(g)—, wherein X is, at each        occurrence, independently selected among —F and —CF₃; b, e and g        are integers up to 100, e>0, b≧0, g≧0; preferably, b and g>0,        e/b is comprised between 0.2 and 5.0 and (e+b)/g is comprised        between 5 and 50;    -   —(C₃F₆O)_(e)—(CFXO)_(g)—, wherein X is, at each occurrence,        independently selected among —F and —CF₃; e and g are integers        up to 100, e>0, g≧0, preferably g>0, e/g being comprised between        5 and 50.

The fluorinated polymer may be a solid or a liquid. When the fluorinatedpolymer is a solid the process may be carried out by directly contactingfluorine and the per(halo)olefin with the polymer in solid form.Preferably the polymer is in the form of granules or pellets to increasethe area of the polymer surface directly in contact with fluorine.

Alternatively, the process may be carried out in the liquid phase bysuspending, dispersing or dissolving the fluorinated polymer in asuitable solvent. The term “dissolved” is intended to denote a “true”solution of the fluorinated polymer. The wording “dispersed form” is onthe other hand intended to denote a colloidal suspension of thefluorinated polymer, whereby particles of the fluorinated polymer ofaverage particle size of generally less than 500 nm are stably suspendedwith no settlement phenomena when left in unperturbed state. In case ofdispersed form, the fluorinated polymer advantageously possesses anaverage particle size of 1 to 500 nm, preferably of 1 to 250 nm, evenmore preferably from 1 to 100 nm. The term “suspension” indicates a truesuspension of the fluorinated polymer granules or pellets into theliquid phase.

When the fluorinated polymer is a liquid at the process temperature, asit is often the case with fluorinated polyethers, the process may becarried out by contacting the starting fluorinated polymer with fluorineand the per(halo)olefin. Alternatively, the liquid fluorinated polymermay be diluted in a suitable solvent.

Typically, the process is carried out in the liquid phase. Suitablesolvents include solvents which are inert towards fluorine gas, such asperfluoroalkanes, perfluoropolyethers, perfluoroethers andperfluorotrialkyl amines.

Fluorine may be fed into the reactor as a pure gas or diluted with aninert gas, such as N₂, Ar and He.

Typically, fluorine and the (per)haloolefin, in separate feeds, arecontinuously added to the fluorinated polymer at the given temperatureof the process. Generally fluorine is added to the reaction in an amounthigher than the stoichiometric amount necessary to convert all theunstable end-groups in the fluorinated polymer to stable end-groups.

The presence of a (per)haloolefin allows carrying out the processaccording to the invention under mild conditions and with highconversion of the unstable end-groups into stable end-groups.

The expression “(per)haloolefin comprising at least one carbon-carbondouble bond and having at least one fluorine or chlorine atom on eitherone of the carbon atoms of said double bond” is intended to encompassfluoroolefins, chloroolefins, and fluorochloroolefins, these compoundspossibly comprising one or more heteroatom different from Cl and F, inparticular oxygen. Preferably the (per)haloolefin is a perfluoroolefin.

In one embodiment (per)haloolefins suitable for use in the process arethose represented by the following formula:

wherein R_(a), R_(b), R_(c) and R_(d) are each independently selectedfrom the group consisting of —F, —Cl and hydrocarbon groups, possiblycomprising one or more chlorine and/or fluorine atoms, optionally havingone or more heteroatoms different from —F and —Cl, e.g. oxygen, possiblydirectly linked to the double bond. At least one of R_(a), R_(b), R_(c)and R_(d) is selected from fluorine or chlorine.

Preferably, R_(a), R_(b), R_(c) and R_(d) are each independentlyselected in the group consisting of —F, —Cl, C₁-C₄ perfluorocarbongroups, C₁-C₄ oxygen-containing perfluorocarbon groups, C₁-C₄fluorochlorohydrocarbon groups, and C₁-C₄ oxygen-containingfluorochlorohydrocarbon groups. Still preferably, R_(a), R_(b), R_(c)and R_(d) are each independently selected in the group consisting of —F,—Cl, C₁-C₂ perfluorocarbon groups, C₁-C₂ oxygen-containingperfluorocarbon groups, C₁-C₂ fluorochlorohydrocarbon groups, and C₁-C₂oxygen-containing fluorochlorohydrocarbon groups. Even more preferablyat least three of R_(a), R_(b), R_(c) and R_(d) are selected from —F,—Cl.

As examples of such (per)haloolefins, mention may be made of C₂-C₁₈fluoro and/or perfluoroolefins, preferably C₂-C₁₀ fluoro and/orperfluoroolefins, such as tetrafluoroethylene, hexafluoropropylene andits dimers and trimers, octafluorobutene, perfluoropentene,perfluorohexene, perfluoroheptene, perfluorooctene,perfluorocyclobutene, perfluorocyclopentene, perfluorocyclohexene,chlorotrifluoroethylene, dichlorodifluoroethylene,chloropentafluoropropene, perfluorobutadiene, perfluoromethylvinylether,perfluoroethylvinylether, perfluoropropylvinylether; CF₃OCCl═CClF,trichloroethylene, tetrachloroethylene, dichloroethylene isomers;fluorodioxoles, of formula (I):

wherein each of R_(f3), R_(f4), R_(f5), R_(f6), equal or different eachother, are as defined above.

Preferably the (per)haloolefin is selected from the group consisting oftetrafluoroethylene, hexafluoropropylene and its dimers and trimers.More preferably the (per)haloolefin is selected from the groupconsisting of tetrafluoroethylene and hexafluoropropylene.

The amount of (per)haloolefin used in the process is not critical.According to one embodiment, the amount of said (per)haloolefin iscomprised in the range of 0.1 to 30 mol % with respect to the amount offluorine fed to the reaction. Preferably, said amount is comprised inthe range of 0.5 to 20 mol % with respect to the amount of fluorine fedto the reaction. More preferably, said amount is comprised in the rangeof 1 to 15 mol % with respect to the amount of fluorine fed to thereaction.

Typically the (per)haloolefin is continuously fed to the reaction systemin the required amount during the fluorination reaction.

A hydrogen fluoride scavenger may be used (e.g. NaF, KF).

The process temperature may be advantageously maintained in the range of−100° C. to +100° C.

Advantageously, no temperature increase is required to perform thecomplete fluorination of the fluorinated polymer.

The end of the reaction can be advantageously detected by onlineanalysis, by checking fluorine conversion, which typically suddenlydrops to zero.

At the end of the process the unstable end-groups are converted intostable —CF₃ groups.

When the fluorinated polymer is selected among those comprisingrecurring units derived from at least one ethylenically unsaturatedfluorinated monomer, the amount of residual unstable end-groups at theend of the fluorination process is of less than 15 mmol of unstableend-groups per kg of fluorinated polymer, less than 12 mmol/kg, and evenless than 10 mmol/kg. At the end of the inventive process fluorinatedpolymers containing less than 5 mmol of unstable end-groups per kg offluorinated polymer, less than 3 mmol/kg of fluorinated polymer and evenless than 1 mmol/kg of fluorinated polymer may advantageously beobtained.

When the fluorinated polymer is selected among fluorinated polyethersthe amount of residual unstable end-groups at the end of thefluorination process is of less than 80 mmol of unstable end-groups perkg of fluorinated polyether, less than 60 mmol/kg, and even less than 50mmol/kg. At the end of the inventive process fluorinated polymerscontaining less than 40 mmol of unstable end-groups per kg offluorinated polyether, less than 30 mmol/kg of fluorinated polyether andeven less than 20 mmol of unstable end-groups per kg of fluorinatedpolyether may advantageously be obtained.

The resulting fluorinated polymers are characterized by an increasedthermal and chemical stability.

The invention will be now described in more detail with reference to thefollowing examples, whose purpose is merely illustrative and notintended to limit the scope of the invention. Should the disclosure ofany patents, patent applications, and publications which areincorporated herein by reference conflict with the description of thepresent application to the extent that it may render a term unclear, thepresent description shall take precedence.

EXAMPLES

¹⁹F-NMR determination of end-groups was carried out according to methodsknown in the art.

The quantitative FT-IR determination of end-groups was carried outaccording to the following analytical method.

Frequency was observed in the following range: 1890-1880 cm⁻¹ for acylfluoride end groups, 1820-1770 cm⁻¹ for carboxylic acid end-groups.Carboxylic acid end-groups generally show two carbonylic bands: thehigher frequency one has been associated with the monomeric form, whilethe lower frequency one to carboxylic groups forming hydrogen bondedsystems. The overall sensitivity of the FT-IR method is in the order of5*10⁻⁵ moles/Kg. Samples, in the physical form of powder or film havebeen analysed with an optical path length in the order of hundreds ofmicrons.

Reference matrixes of fluorinated polymers with no end-groups, to beused as references for spectral subtraction, were identified with the IRmethod described previously in PIANCA, M., et al. End groups influoropolymers. J. Fluorine Chem. 1999, vol. 95, p. 71-84.

Experimental details: IR data recorded in Transmission, with a ThermoNicolet Nexus® FT-IR equipment (256 scans, resolution 2 cm⁻¹).

After spectral recording, the spectral subtraction were performed usingthe corresponding reference matrixes for each polymer; spectral rangeconsidered for end-groups evaluation was 2000-1600 cm⁻¹ for carbonylregion (3600-3500 cm⁻¹ for OH groups of carboxylic acid in monomericform if necessary). Frequencies and intensities observed in thesubtraction spectra were used for quantitative evaluation of theunstable end-groups.

Example 1 and Comparative Example 1 Fluorination of a FluorinatedPolyether Having Mn=4725

The starting fluorinated polymer was a perfluorinated polyether mixturehaving generic formula FC(O)CF₂O(CF₂CF₂O)_(b′)(CF₂O)_(a′)CF₂C(O)F and anumber average molecular weight of 4725 g/mol.

In a 500 ml stainless steel reactor 400 g of perfluorinated polyetherwere loaded and heated at 80° C. while keeping the system under vigorousstirring. At t=0 h fluorine (6.3 NI/h in 4.0 NI/h of He) and C₃F₆ (0.3NI/h in 2.0 NI/h of He) were fed to the reactor through two inlet pipes.During the reaction, small samples of the mixture were taken at regularintervals and analyzed via ¹⁹F-NMR to determine the residual —COFconcentration. After 26.5 hours the reaction was stopped and thereaction mixture analyzed. Table 1 reports the —COF concentration as afunction of time.

TABLE 1 Time —COF concentration (h) (mmol/kg) 0 139 5.5 102 12.5 71 19.554 26.5 36

The same procedure was repeated without the addition of C₃F₆. Table 2reports the —COF concentration as a function of time.

TABLE 2 Time —COF concentration (h) (mmol/kg) 0 139 7.8 122 16 105 23.996 30.4 83

The comparison of the data in Tables 1 and 2 shows that the presence ofC₃F₆ during the fluorination process unexpectedly increases by 2-foldthe efficiency of the unstable end-groups conversion.

Example 2 and Comparative Example 2 Fluorination of a FluorinatedPolyether Having Mn=506

Following the same procedure of Example 1, 140 g of a perfluorinatedpolyether mixture having generic formulaFC(O)CF₂O(CF₂CF₂O)_(b′)(CF₂O)_(a′)CF₂C(O)F and a number averagemolecular weight of 506 g/mol was fluorinated in the presence of C₃F₆.Fluorine (4.0 NI/h in 9.0 NI/h of He) and C₃F₆ (0.3 NI/h in 9.0 NI/h ofHe) were fed to the reactor held at 20° C. and the residual —COF groupsmonitored by ¹⁹F-NMR. After 15 hours the reaction was stopped and thereaction mixture analyzed. Table 3 reports the —COF concentration as afunction of time.

TABLE 3 Time —COF concentration (h) (mmol/kg) 0 3509 7 754 15 22

After 15 hours 99.4% of the unstable —COF groups were converted toneutral, stable end-groups

The same procedure described in Example 2 was repeated without theaddition of C₃F₆. After 15 hours the —COF conversion to neutralend-groups was below 5%.

Examples 3 and 4 Fluorination of a Fluorinated Polyether Having Mn=506in the Presence of C₂F₄ or C₂F₃Cl

Following the same procedure of Example 2, 147 g of the perfluorinatedpolyether mixture having generic formulaFC(O)CF₂O(CF₂CF₂O)_(b′)(CF₂O)_(a′)CF₂C(O)F and an average molecularweight of 506 g/mol was fluorinated in the presence of C₂F₄ or C₂F₃Cl.Fluorine (4.0 NI/h in 9.0 NI/h of He) and C₂F₄ or C₂F₃Cl (0.3 NI/h in9.0 NI/h of He) were fed to the reactor held at 20° C. and the residual—COF groups monitored by ¹⁹F-NMR. After 15 hours the reaction wasstopped and the reaction mixture analyzed. Table 4 reports the —COFconcentration as a function of time.

TABLE 4 —COF concentration (mmol/kg) Time Example 3 Example 4 (h) C₂F₄C₂F₃Cl 0 3509 3509 7 880 852 15 53 35

After 15 hours 98.5% (Example 3) and 99.0% (Example 4) of the unstable—COF groups were converted to neutral, stable end-groups.

Example 5 and Comparative Example 3 Fluorination of atetrafluoroethylene/2,2,4-trifluoro-5-trifluoromethoxy-1,3-dioxolecopolymer

A solution of 20 g of atetrafluoroethylene/2,2,4-trifluoro-5-trifluoromethoxy-1,3-dioxolecopolymer in a 60/40 molar ratio (commercially available under the tradename of Hyflon® AD 40, Solvay Solexis SpA) in perfluorinated polyethersolvent (Perfluoropolyether Galden® LS165, Solvay Solexis SpA) wasfluorinated in a stirred PFA flask at 20° C. Fluorine (1.8 NI/h in 5.4NI/h of He) and C₃F₆ (0.3 NI/h in 0.9 NI/h of He) were separately fedinto the stirred solution. After 10 h and 20 h of fluorination twosamples were taken, solvent was evaporated and the dry polymer wascharacterized via FT-IR according to the method described above toverify the presence of end-groups. After 20 h no residual unstableend-groups were detected. Table 5 shows the concentration of unstableend-groups as a function of time of fluorination in terms of mmol/kg.

TABLE 5 Rf—COOH Rf—COOH Rf—COF t (1814 cm⁻¹) (1776 cm⁻¹) (1884 cm⁻¹)(hours) (mmol/kg) (mmol/kg) (mmol/kg) 0 3.5 1.2 0.0 10 0.0 0.0 0.5 200.0 0.0 0.0

The same procedure was repeated without the addition of C₃F₆. After 20hours the reaction was stopped and the content of unstable end-groupsanalysed by FT-IR. The results reported in Table 6 show that residualunstable end-groups are still present in the fluorinated polymer evenafter 20 hours of reaction.

TABLE 6 Rf—COOH Rf—COOH Rf—COF t (1814 cm⁻¹) (1776 cm⁻¹) (1884 cm⁻¹)(hours) (mmol/kg) (mmol/kg) (mmol/kg) 0 3.5 1.2 0.0 20 0.0 0.0 0.9

Example 6 Fluorination of tetrafluoroethylene/CF₂═CFOCF₂CF₂SO₂FCopolymer

A solution of 7.5 g of a tetrafluoroethylene/CF₂═CFOCF₂CF₂SO₂F copolymerhaving an equivalent weight of 550 g/eq in perfluoroeptane wasfluorinated in a stirred PFA flask at 0° C. Fluorine (1.8 NI/h in 5.4NI/h of He) and C₃F₆ (0.3 NI/h in 0.9 NI/h of He) were separately fedinto the stirred solution. After 6 h the solvent was evaporated and thedry polymer was characterized via FT-IR. Table 7 shows the concentrationof residual unstable end-groups as a function of time in terms ofmmol/kg. After 6 hours all the unstable end-groups have been converted.

TABLE 7 Rf—COOH Rf—COOH Rf—COF t (1814 cm⁻¹) (1776 cm⁻¹) (1884 cm⁻¹)(hours) (mmol/kg) (mmol/kg) (mmol/kg) 0 3.9 2.7 0.0 6 0.0 0.0 0.0

Possible modifications and/or additions may be made by those skilled inthe art to the hereinabove disclosed and illustrated embodiment whileremaining within the scope of the following claims.

The invention claimed is:
 1. A process for reducing the amount ofunstable end-groups in a fluorinated polymer, the process comprisingreacting a fluorinated polymer comprising unstable end-groups withfluorine in the presence of at least one (per)haloolefin comprising atleast one carbon-carbon double bond and having at least one fluorine orchlorine atom on either one of the carbon atoms of said double bond. 2.Process according to claim 1 wherein the unstable end-groups areselected from end groups comprising a —C(O)— functional group. 3.Process according to claim 1 wherein the fluorinated polymer is selectedfrom polymers comprising recurring units derived from at least oneethylenically unsaturated fluorinated monomer selected from the groupconsisting of: C₂-C₈ perfluoroolefins; chloro- and/or bromo- and/oriodo-C₂-C₆ fluoroolefins; fluoroalkylvinylethers of formulaCF₂═CFOR_(f1) in which R_(f1) is a C₁-C₆ perfluoroalkyl;fluoro-oxyalkylvinylethers of formula CF₂═CFOX₁, in which X₁ is a C₁-C₁₂fluoroxyalkyl, or a C₁-C₁₂ perfluorooxyalkyl having one or more ethergroups; fluoroalkyl-methoxy-vinylethers of formula CF₂═CFOCF₂OR_(f2) inwhich R_(f2) is a C₁-C₆ fluoro- or perfluoroalkyl or a C₁-C₆perfluorooxyalkyl having one or more ether groups; functionalfluoro-alkylvinylethers of formula CF₂═CFOY₀, in which Y₀ is a C₁-C₁₂fluoroalkyl or perfluoroalkyl, or a C₁-C₁₂ fluorooxyalkyl, or a C₁-C₁₂perfluorooxyalkyl, said Y₀ group having one or more ether groups and Y₀comprising a carboxylic or sulfonic acid group, in its acid, acid halideor salt form; fluorodioxoles, of formula (I):

wherein each of R_(f3), R_(f4), R_(f5), R_(f6), equal or different eachother, is independently a fluorine atom, a C₁-C₆ fluoro- orper(halo)fluoroalkyl, optionally comprising one or more oxygen atom. 4.Process according to claim 3 wherein the fluorinated polymer is selectedfrom the group consisting of polymers comprising recurring units derivedfrom tetrafluoroethylene and recurring units derived from at least oneother monomer selected from the group consisting of hexafluoropropyleneand/or perfluoro(alkyl vinyl ether) wherein the perfluoroalkyl group ofthe perfluoro(alkyl vinyl ether) is linear or branched and contains 1 to5 carbon atoms; polymers comprising recurring units derived fromtetrafluoroethylene or chlorotrifluoroethylene and recurring unitsderived from fluorodioxoles of formula (I); polymers comprisingrecurring units derived from tetrafluoroethylene and/orchlorotrifluoroethylene and recurring units derived from at least onefunctional monomer of formula CF₂═CF—O—(CF₂CF(CF₃)O)_(m)—(CF₂)_(n)SO₂Fand its acid or salt form wherein m is an integer equal to 0 or 1, and nis an integer from 0 to
 10. 5. Process according to claim 1 wherein thefluorinated polymer is selected form fluorinated polyethers comprisingat least one recurring unit selected from the group consisting of:—CFXO—; —CF₂CFXO—; —CFXCF₂O—; —CF₂CF₂CF₂O—; —CF₂CF₂CF₂CF₂O—; and—(CF₂)_(k)—CFZ—O—, wherein k is an integer from 0 to 3 and Z is a groupof general formula —OR_(F)T₃, wherein R_(F) is a fluoropolyoxyalkylenechain comprising a number of recurring units from 0 to 10, saidrecurring units being chosen from the group consisting of: —CFXO—,—CF₂CFXO—, —CF₂CF₂CF₂O—, —CF₂CF₂CF₂CF₂O—, wherein T₃ is a C₁—O₅perfluoroalkyl group and wherein each of X is independently —F or —CF₃.6. Process according to claim 5 wherein the fluorinated polymer isselected from the fluorinated polyethers comprising units selected fromthe group consisting of:—(CF₂O)_(a)—(CF₂CF₂O)_(b)—(CF₂—(CF₂)_(d)—CF₂O)_(c), wherein a, b and care integers up to 100, and d is independently at each occurrence aninteger equal to 1 or 2; a

0, b

0, c

0 and a+b>0; —(C₃F₆₀)_(e)—(CF₂CF₂O)_(b)—(CFXO)_(g)—, wherein X is, ateach occurrence, independently selected among —F and —CF₃; b, e and gare integers up to 100, e>0, b

0, g

0; and —(C₃F₆₀)_(e)—(CFXO)_(g)—, wherein X is, at each occurrence,independently selected among —F and —CF₃; e and g are integers up to100, e>0, g


0. 7. Process according to claim 1 wherein the (per)haloolefin complieswith the following formula:

wherein R_(a), R_(b), R_(c) and R_(d) are each independently selected inthe group consisting of F, Cl and hydrocarbon groups, wherein thehydrocarbon group optionally comprises one or more chlorine and/orfluorine atoms, and optionally includes one or more heteroatomsdifferent from fluorine and chlorine, optionally directly linked to thedouble bond.
 8. Process according to claim 7, wherein R_(a), R_(b),R_(c) and R_(d) are each independently selected from the groupconsisting of —F, —Cl, C₁-C₄ perfluorocarbon groups, C₁-C₄oxygen-containing perfluorocarbon groups, C₁-C₄ fluorochlorohydrocarbongroups, and C₁-C₄ oxygen-containing fluorochlorohydrocarbon groups. 9.Process according to claim 1 wherein the (per)haloolefin is selectedfrom the group consisting of: tetrafluoroethylene, hexafluoropropyleneand its dimers and trimers, octafluorobutene, perfluoropentene,perfluorohexene, perfluoroheptene, perfluorooctene,perfluorocyclobutene, perfluorocyclopentene, perfluorocyclohexene,chlorotrifluoroethylene, dichlorodifluoroethylene,chloropentafluoropropene, perfluorobutadiene, perfluoromethylvinylether,perfluoroethylvinylether, perfluoropropylvinylether; CF₃OCCl═CClF,trichloroethylene, tetrachloroethylene; and fluorodioxoles of formula(I).
 10. Process according to claim 1 wherein the amount of said(per)haloolefin is in the range of 0.1 to 30% moles with respect to theamount of fluorine.
 11. Process according to claim 3 comprising reducingthe amount of unstable end-groups in the fluorinated polymer to lessthan 5 mmol of unstable end-groups per kg of fluorinated polymer. 12.Process according to claim 5 comprising reducing the amount of unstableend-groups in the fluorinated polymer to less than 80 mmol of unstableend-groups per kg of fluorinated polymer.
 13. Process according to claim1 carried out in the liquid phase.
 14. Process according to claim 4comprising reducing the amount of unstable end-groups in the fluorinatedpolymer to less than 5 mmol of unstable end-groups per kg of fluorinatedpolymer.
 15. Process according to claim 6 comprising reducing the amountof unstable end-groups in the fluorinated polymer to less than 80 mmolof unstable end-groups per kg of fluorinated polymer.
 16. Processaccording to claim 6 wherein the fluorinated polymer is selected fromthe fluorinated polyethers comprising units selected from the groupconsisting of: —(CF₂O)_(a)—(CF₂CF₂O)_(b)—(CF₂—(CF₂)_(d)—CF₂O)_(c),wherein a, b and c are integers up to 50; d is independently at eachoccurrence an integer equal to 1 or 2; a>0, b>0, c

0, and b/a is between 0.1 and 10; —(C₃F₆O)_(e)—(CF₂CF₂O)_(b)—(CFXO)_(g)—wherein X is, at each occurrence, independently selected from —F and—CF₃; b, e and g are integers up to 100; e>0, b>0, g>0, e/b is between0.2 and 5.0, and (e+b)/g is between 5 and 50; and—(C₃F₆O)_(e)—(CFXO)_(g)—, wherein X is, at each occurrence,independently selected from —F and —CF₃; e and g are integers up to 100;e>0, g>0, and e/g is between 5 and 50.